Apparatus for refining molten iron and molten iron alloys

ABSTRACT

A ladle containing molten iron or molten iron alloys is located beneath a supporting frame, the supporting frame including a movable stirring shaft carrying at least one stirring rod at the lower end thereof, the stirring rod being adapted to extend only into the upper layer portion of the molten iron in the ladle. At least one oxygen blowing lance is connected to the supporting frame and means for supplying a predetermined quantity of reactant into the ladle is provided. The stirring shaft is moved relative to the frame, and preferably, in a swinging manner whereby at least a point on the stirring shaft axis moves along a substantially circular path.

United S'tatesPatent [191 Ando et a1.

1 1] 3,729,183 [451 Apr. 1973 APPARATUS FOR REFINING MOLTEN IRON AND MOLTEN IRON ALLOYS 73 Assignee: Nippon Kokan Kabushiki Kaisha,

Tokyo, Japan [22] Filed: Feb. 26, 1971 [21] Appl. No.: 119,221

Related us. Application new [62] Division of Ser, No. 818,283, April 22, 1969, Pat

[30] Foreign Application Priority Data Ap. 22, 1969 Great Britain ..20,4l6/69 Ap. 24, 1969 Germany ..P 19 20 958.6 Ap. 24, 1969 France ..69l2993 Ap. 23, 1969 Canada i ..49,493 Ap. 24, 1969 Australia... ..540l3/69 Ap. 24, 1969 U.S.S.R. ..l324512 Ap. 24, 1969 U.S.S.R. ..208320 Ap. 23, 1969 1 Netherlands ..6906228 [52] 11.8. CI ...266/34 A, 75/45, 75/61 "[51] Int. Cl.....' ,.C2lc 7/00 [58] Field of Search ..266/34 A, 34 L, 34 LM,

[56] References Cited UNITED STATES PATENTS 3,459,536 8/1969 Touzalin, ..266/34 A x 3,194,650 7/196'5 Kurzinski.. 1.75/60 X 2,677,609 5/1954 Moore ....266/34 A X 2,820,707 l/l958 Walker ....266/34 L 2,390,052 12/1945 Bemstorff..... ....266/34 A 2,817,584 12/1957 Kootz ..75/60 3,150,963 9/ 1964 Kurzinski .t ..75/60 Primary Examiner-J. Spencer Over'holser Assistant Examiner.1ohn S. Brown AttorneyFlynn & Frishauf [57] ABSTRACT A ladle containing molten iron or molten iron alloys is located beneath a supporting frame, the supporting frame including a movable stirring shaft carrying at least one stirring rod at the lower end thereof, the stirring rod being adapted to extend only into the upper layer portion of the molten iron in the ladle. At least one oxygen blowing lance is connected to the supporting frame and means for supplying a predetermined quantity of reactant into the ladle is provided. The

stirring shaft is moved, relative to the frame, and,

6 Claims, 2 Drawing Figure s Patented April 24, 1973 2 Sheets-Sheet l Patnted April 24, 1973 3,729,183

2 Sheets-Sheet 2 FIG.2

. APPARATUS FOR REFINING MOLTEN IRON AND MOLTEN IRON ALLOYS RELATED APPLICATION:

This application is a division of application Ser. No. 818,283, now U.S. Pat. No. 3,664,827 filed Apr. 22, 1969.

BACKGROUND OF THE INVENTION This invention relates to a novel method and apparatus for refining molten iron or iron alloys and more particularly to a method and apparatus for rapidly removing impurities in molten pig iron, especially phosphorus and sulphur by causing it to react with oxygen and slag. Thus, the invention contemplates to readily remove such impurities as phosphorus, sulphur and chromium and the like while limiting to the minimum the variation of other components, especially in the order of silicon and carbon, and that during the.

final stage of decarburization the quantity of phosphorus, chromium, etc., decreases. Thus, with ox- 1 ygen, it is impossible to rapidly refine low phosphorus, high carbon steel. However, where a slag is prepared which is suitable to remove phosphorus and chromium at low temperature and the molten iron is caused to react with such a slag it is possible to remove phosphorus, chromium and the like in preference to decarburization. However, as shown by the following equation, the dephosphorization reaction generally requires supply of oxygen:

For example, to reduce the quantity of phosphorus from 0.2 to 0.05 percent, 1.93Kg (1.35Nm") of oxygen per ton of molten metal pig iron is required. In order to perform rapid refining operation, it is desirable to blow oxygen in the form of pure oxygen or of air onto the surface of the molten pig iron through a lance. In this case, however, the temperature of the surface portion of the molten iron with oxygen being flown thereinto increases extremely, thus causing easy decarburization. Accordingly, in such a case, it has been known in the art to cause slag, which is advantageous for dephosphorization reaction, to contact with the molten iron over as wide area as possible and over constantly renewed surface so as to enhance the movement of the molten iron to prevent excess rise in the temperature at the surface to which oxygen is blown and to bring the supplied oxygen into dephosphorization reaction as fast as possible.

Based on these considerations, the shaking ladle method, proposed. Further, in the steel manufacturing furnace soft blow refining with a L.D. converter has been practiced by utilizing a portion of above described con-v siderations. Of these the shaking ladle method involves rotor method and the like have been imparting eccentric motion to a container of the molten pig iron or the ladle itself for the purpose of increasing the speed of movement of the molten pig iron and to increase the contact surface between the slag and the molten iron. Accordingly, splash of the slag and molten pig iron becomes excessive which requires an excessively large container so that practical use of this method is limited.

The rotor method and the like do not result in rapid and sufficient dephosphorization. Moreover, any of these methods requires additional process steps to the existing refining steps, so thatthey are difficult to practice.

The soft blow refining process with a L.D. converter requires a refining time twice as long as the ordinary refining time. In addition, even when the slag is sufficiently removed initially, since a substantial quantity of slag remains adhered to the furnace body there is a problem that phosphorus is again entrained in the iron during the finishing refining step.

SUMMARY OF THE INVENTION It is therefore an object of this invention to provide a novel method and apparatus capable of removing impurities, especially phosphorus and sulfur from molten iron or iron alloys without the accompanying various difficulties described above.

According to this invention, use is made of a considerable inertia and convection of the molten pig iron existing after pouring it into a ladle and the mechanical stirring is limited to the area receiving the blown oxygen and the area near the contact surface between the slag and the molten pig iron, or to only the upper layer portion of the molten pig iron. In addition, in order to minimize the splash, means are used to create a plurality of small stirring whirls or eddies. With this invention, even when a ladle is charged to about to percent of its normal capacity, it is possible to perform a satisfactory refining operation so that the invention is readily applicable to the existing molten iron transfer step. Briefly stated, the apparatus of this invention comprises a mechanism for stirring the upper layer portion of the molten pig iron, a mechanism for blowing oxygen onto the surface of the molten pig iron, and a mechanism for charging a reactant into a ladle containing the molten pig iron.

BRIEF DESCRIPTION OF THEDRAWING Other features and objects of this invention, the mechanism and operation thereof can be more fully understood from the following detailed description when taken in conjunction with the accompanying drawing in which:

FIG. 1 is a plan view of the apparatus embodying this invention, and;

FIG. 2 shows a vertical sectional view of the apparatus shown in FIG. 1 in which the left hand half shows a section taken along a line Ila-Ila and the right hand half shows a section taken along a line IIb-IIb in FIG. 1.

Referring now to the accompanying drawing, a ladle for receiving molten pig iron and mounted on a suitable carriage is disposed substantially below the center of a treating table supporting frame 1. Stirring rods 3 of carbonaceous material or other suitable refractory materi- .al are arranged in the upper portion of the ladle 2. Stirring rods 3 are secured to a disc 5 at the lower end of a stirring shaft 4 so that when the shaft 4 is lowered, the stirring rods 3 are immersed into the upper portion of the molten pig iron kept in the ladle. The stirring shaft 4 is connected to a swinging frame 7 provided with three radial arms 6 and the vertical movement of shaft 4 is effected by a motor 8 connected to the swinging frame 7 through a reduction gearing. At the lower side of the free end of each arm 6 is projected a stub shaft 9. A shaft 11 driven through a suitable transmission mechanism by a motor mounted on the treating table supporting frame 1 is provided thereon and the stub shafts 9 and the shaft 11 are interconnected with suitable eccentricity, for example, of 150mm. 'Accordingly, as themotor 10 is energized'to drive the shaft through the transmission mechanism, the stub shaft 9 will berotated about the axis of the shaft 11 with a radiuscorresponding to said eccentricity. In this manner, as the respective stub shafts 9 are rotated eccentrically about the axis 1 l, the axis of stirring shaft 4 'will be moved along a circle through arms 6 and the swinging frame 7, thus imparting a circular motion to stirring rods 3 to effect stirring of the surface of th molten pig iron.

The oxygen blowing mechanism comprises water cooled lances suspended from a supporting structure 1 2 upstanding from the treating table supporting frame L -The water cooled lances include a first lance 13 which extends through a guide 14. First lance 13 is vertically moved by a suspension wire and is fixed to guide 14 by means of a handle 16. A second lance 13' which extendsthrough a guide 14 secured to the stirring shaft 4, is vertically moved by asuspension wire 15 and is secured to the stirring shaft 4 by means of a handle 16. In this example, the number of first lances 13 that are fixed to the treating table supporting frame is three whereas .the number of second lances 13 secured to swinging shaft 4 is one. Oxygen is supplied to the treating table supporting frame 1 through a conduit l7, and distribution pipes 18 branched from the conduit 17 are connected to lances 13 and 13' via flexi ble pipes 19 to blow oxygen onto the upper surface of the molten pig iron through the lower ends of lances l3 and 13.

The reactant charging device includes a bucket 20 suspended from a hoist 21 movable along a beam 22 on the treating table supporting frame 1. The bucket 20 operated by the hoist 21 is used to supply the reactant ing a stirring mechanism, an oxygen blowing mechanism and a reactant charging mechanism wherein oxygen is blown upon the surface of the molten pig iron through lances l3 and 13' while the surface layer portion of the molten pig iron is stirred by the operation of a motor 10 and wherein the reactant is continuously charged while the molten iron is stirred and the oxygen is blown. Accordingly, since only the surface layer portion is stirred, the power required for this purpose may be relatively small particles, thus reducing the cost of installation. in addition, it is possible to blow a largequantity of oxygen at high efficiencies. As the pressure of blowing oxygen is low, the slag forming agent may be in the form of small granules which not only increases the speed of forming the desired slag but also enables readily adjustments of slag composition and temperature. Further, it is possible to employ existing ladies without the necessity of changing the process steps. 1

Thus, this invention provides a novel method .of refining iron and ironalloys which can readily and rapidly remove impurities therein and improves the efficiency of oxygen and reactants so that ordinary pig iron for cast iron and for steel manufacturing can be readily converted into pig iron of low phosphorus and sulphur content at very low cast.'This also enables manufacture with converters species of steel which heretobefore could be obtained only with electric furnaces. Similarly, when pig iron of low phosphorus and sulphur content or low silicon content is prepared with electric furnaces, it becomes possible to charge a large quantity of the pig iron into the electric furnace thus decreasing electric power and hence cost of the raw material. Further it is possible to increase the efficiency of steel manufacturing and the useful life of expensive refractories utilized in the furnace.

While the invention has been shownand described in terms of its preferred embodiment, it will be clearto those skilled in the art that many alterations and modifications may be made. within the true spirit and scope of the invention. For'example, it is possible to refine iron by the method of the present invention either simultaneously with or after desulphurization of pig iron. A plurality of lances for blowing oxygen may be provided aslant to the treating table supporting frame so as to blow oxygen from the upper corner of the ladle; and the location of said lance is not limited to that herein defined i.e., in the axis of stirring shaft.

The decrease of carbon in the molten iron is small in the present refining method because the main object of the invention lies in the refining of impurities, and not in the decarburization of major carbon content.

We claim:

1. Apparatus for refining molten iron or molten iron alloys comprising a supporting frame and a ladle disposed beneath said supporting frame and adapted to contain said molten iron, said supporting frame includmg:

a movable stirring shaft carrying at least one stirring rod at the lower end thereof, said stirring rod extending only into the upper layer portion of the molten iron in said ladle during operation;

means to impart movementto said stirring shaft;

an oxygen blowing lance connected to said supporting frame and extending through said stirring shaft to blow oxygen to the upper surface of said molten metal during movement of said shaft; and means to continuously supply a predetermined quantity of a reactant into said ladle. 2. Apparatus according to claim 1, wherein said stirring shaft is movable in the vertical direction.

3. Apparatus according to claim 1, wherein said stirring shaft is movable relative to said frame.

4. Apparatus according to claim 1, wherein said movementmeans imparts a swinging movement to said stirring shaft relative to said supporting frame. 

2. Apparatus according to claim 1, wherein said stirring shaft is movable in the vertical direction.
 3. Apparatus according to claim 1, wherein said stirring shaft is movable relative to said frame.
 4. Apparatus according to claim 1, wherein said movement means imparts a swinging movement to said stirring shaft relative to said supporting frame.
 5. Apparatus according to claim 1, wherein said movement means moves said stirring shaft such that at least a point on the longitudinal axis of said stirring shaft moves along a substantially circular path.
 6. Apparatus according to claim 5, wherein said supporting frame further comprises eccentric driving means coupled to said stirring shaft to cause said stirring shaft axis point to move along said substantially circular path. 